This invention relates generally to integrated services digital networks (ISDN), and particularly to accommodating analog and digital equipment over existing wiring in a subscriber premise (office, house, etc.) having a single line ISDN subscription.
ISDN is defined by internationally accepted standard digital network user interfaces. The resulting network offers a variety of subscriber access lines capable of supporting services including voice, data, facsimile, and video. There are two CCITT (International Telegraph and Telephone Consultative Committee) recommended standard integrated services digital network interfaces for user access. They include the basic rate interface (BRI) and a primary rate interface (PRI). By integrating these various services on a single transport system means, the subscriber avoids buying multiple services to meet multiple service needs. As a practical consideration a single transport system requires less overhead than providing a discrete access line for each service, and results in a total lower cost of service.
An ISDN Basic Rate Interface (BRI) consists of three channels, referred to as two B channels plus a D channel (2B+D), in which all signals flowing over the external TELCO lines are carried in a baseband digital form and in a standardized frame format. With this arrangement, the B channels are the basic user channels which carry digital voice, high-speed data, and other functions at a maximum channel rate of 64 kbps. The D channel bit rate in this interface is 16 kbps and may serve two purposes. First, the D channel carries control signalling information to control circuit-switched calls on associated B channels at the user interface. In addition, the D channel may be used for packet switching or low speed telemetry when not carrying signalling information. Accordingly, an ISDN Primary Rate Interface (PRI) consists of multiple B channels and one 64 kbps D channel having primary rates of either 1544 kbps (23 B+D) and 2048 kbps (30 B+D).
The BRI may be arranged to provide simultaneous voice and data services in several ways giving users flexibility in configuring their services. A user may use each B channel for voice service, for circuit switched data transport, or for packet switched data services. The D channel can carry packet switched data which interleaves data packets with signaling packets. The BRI may provide a maximum of either two data B channels or one voice B channel and another voice or data channel.
Typically, a single line subscriber premise is wired with two discrete pairs of wires, sometimes referred to as plain old telephone service (POTS). In the POTS configuration, one pair of signal wires (typically green and red) provides a communication path between analog terminal equipment and a junction box that interfaces to external telco wiring. Another pair of signal wires (typically black and yellow) provides a second, or spare, path between analog terminal equipment and the external junction box.
Coexistence between analog and digital terminal equipment at a customer premise has heretofore been impractical. As one solution, discrete digital and analog classes of service to the subscriber premise are provided in order to offer support to both analog and digital devices. Thus, when a single line subscriber elects to add ISDN service, the junction box connection (between, for example, the green/red wires and external TELCO lines) typically remains fixed, but internal POTS wiring is either bypassed or elaborately modified in order to provide a communication path for digital ISDN signals if only one pair of pre-existing wires exists. This solution requires not only bypassing or elaborately modifying the existing POTS wiring, but it also requires maintaining and paying for two discrete classes of service.
As an alternate solution, a single line subscriber may elect to convert from an analog to a digital class of service. In that scenario, the subscriber premise is converted to accommodate digital terminal equipment only. In so doing, the subscriber is compelled to scrap pre-existing conventional telephone (POTS) wiring and terminal equipment, which had effectively become useless, in order to maintain a single (digital) class of service.
Accordingly, it is an object of the present invention to provide an architecture and apparatus that offers a single line communication path between digital and analog devices of a single subscriber and an external ISDN network, through existing internal POTS wiring. It is a further object of the present invention to provide an architecture and apparatus which supports concurrent service to both digital and analog devices through existing POTS wiring.